S2 (Pelvis)

The second sacral vertebra (S2) is the second bone of the sacrum, counting from the top down. It is one of the five individual vertebrae that fuse together to form the sacrum. The sacrum is a triangular bone located at the base of the spine, between the two hip bones, and forms the back wall of the pelvic cavity. S2 is slightly larger than the vertebrae above it, and it has a prominent transverse process on each side that connects to the pelvis. S2 nerves primarily affect the back of the thighs.